Pump control mechanism

ABSTRACT

The invention relates to a control mechanism for a swash plate type pump wherein the cam plate can be moved to opposite inclinations relative to the axis of the rotation of the rotor. An axially movable pump stroke controlling member is connected to means for setting the member through a means permitting lost motion against the action of a spring or the like. A piston subjected to the output pressure of the pump is provided with an arm to coact with an abutment controlling member, when the pump output pressure exceeds a predetermined value with the cam plate of the pump set at one inclination to the axis of rotation. A lever connected to the piston coacts with the abutment in reducing the stroke of the pump when the pump output pressure exceeds a predetermined value with the cam plate of the pump set at the other inclination to the axis of rotation of the rotor.

United States Patent [191 Walmsley May 29, 1973 p [54] PUMP CONTROL MECHANISM [75] Inventor: Robert Edwin Walmsley, Marlow,

England 22' Filed: Dec.29, 1971 211 Appl.No.: 213,475

Related U.S. Application Data [63] Continuation-impart of Ser. No. 866,253, Oct. l4,

1969, abandoned.

5/1951 Moon ..4l7/28l FOREIGN PATENTS OR APPLICATIONS 720,238 lO/l965 Canada ..9l/505 Primary ExaminerWilliam L. Freeh Assistant Examiner-G. La Pointe Attorney-Holman & Stern [57] ABSTRACT The invention relates to a control mechanism for a swash plate type pump wherein the cam plate can be moved to opposite inclinations relative to the axis of the rotation of the rotor. An axially movable pump stroke controlling member is connected to means for setting the member through a means permitting lost motion against the action of a spring or the like. A piston subjected to the output pressure of the pump is provided with an arm to coact with an abutment controlling member, when the pump output pressure exceeds a predetermined value with the cam plate of the pump set at one inclination to the axis of rotation. A lever connected to the piston coacts with the abutment in reducing the stroke of the pump when the pump output pressure exceeds a predetermined value with the cam plate of the pump set at the other inclination to the axis of rotation of the rotor.

3 Claims, 3 Drawing Figures PATENTED HAY 2 91975 SHEET 1 [IF 3 PAIENIED W29 ma 736 7 3 sum 2 OF 3 PUMP CONTROL MECHANISM This is a continuation-in-part of Ser. No. 866,253, filed Oct. 14, 1969, now abandoned.

This invention relates to mechanism for controlling the stroke of a swash-plate type pump of the kind wherein the cam plate can be moved to opposite inclinations relative to the axis of rotation of the rotor so as to provide for a reverse flow of fluid through the pump.

The object of the invention is to provide a convenient control mechanism for such a pump whereby the stroke of the pump will be varied from a predetermined value dependent on the output pressure of the pump. As the torque and hence the horsepower absorbed or developed by the pump is a function of pump displacement or stroke and the delivery pressure of the hydraulic medium the control mechanism provides a substantially constant horsepower control.

According to the invention control mechanism for a pump of the kind specified comprises in combination an axially movable pump stroke controlling member, an abutment on the member, control means for setting said member, means permitting lost motion between the control means and the member against the action of resilient means, a piston subjected to the output pressure of the pump, an arm connected to the piston to co-act with the abutment in reducing the stroke of the pump against the action of said resilient means, when the pump output pressure exceeds a predetermined pressure with the cam plate of the pump set at one inclination to the axis of rotation of the rotor, and a lever connected to the piston so as to co-act with the abutment in reducing the stroke of the pump against the action of said resilient means, when the pump output pressure exceeds sad predetermined pressure with the cam plate of the pump set at the other inclination to the axis of rotation of the rotor.

In the accompanying drawings:

FIG. 1 is a longitudinal sectional view of a known form of pump in association with which mechanism according to the invention can be used,

FIG. 2 is a longitudinal sectional view of mechanism in accordance with the invention, and

FIG. 3 is an end view of the pump seen in FIG. 1, to which the mechanism shown in FIG. 2 has been fitted, a small portion of the drawing being shown in section.

Referring first to FIG. 1 of the drawings, a known form of pump comprises a housing containing a rotor 11 which can be driven by means of a shaft 12. In the rotor 11 are formed a plurality of annularly arranged cylinders containing pistons 13 which co-act with a cam plate 14 which can be angularly adjusted by means of a servo piston 15 situated in a cylinder formed in the housing 10. The cylinders formed in the rotor 11 communicate at their ends remote from the cam plate 14 in turn with an inlet and outlet as the rotor rotates.

The cam plate 14 can be moved to opposite inclinations relative to the axis of rotation of the rotor, so as to provide for a reverse flow of fluid through the pump. The adjustment of the angular setting of the cam plate 14 is effected by the piston 15 under the control of a spool valve 16 which is connected to a control rod 17 which can be moved axially to effect control of the piston 15 by manual or other means.

The end of the cylinder containing the piston 15 remote from the rod 17 is connected through a passage 44 and a selector valve (not shown) to whichever is at the higher pressure of the inlet and outlet of the pump.

Within the piston 15 is a fixed sleeve 45 in which the spool valve 16 is axially movable. Moreover, within the sleeve 45 are formed ports 18 which are in communication with the passage 44 through a passage 46 in the piston. When it is required to move the piston 15 to the right as viewed in FIG. 1, the spool valve 16 is set to the position shown in which a groove 19 in the spool valve communicates with the ports 18. The groove 19 is in communication with an axial bore 21 in the spool valve through which fluid can flow to the left-hand side of the piston 15 as viewed in FIG. 1. Since the pressure at the left-hand side of the piston will act upon the whole area of the piston, whilst the pressure at the right-hand side of the piston 15 acts only on the relatively small annular area of the piston, the piston will move to the right until the ports 18 are removed from the groove 19. It will be appreciated therefore, that in order to move the piston 15 continuously to the right as viewed in FIG. 1, a continual pressure must be applied to the rod 17 to cause the spool valve to maintain its illustrated relationship to the piston. It will also be understood that such movement of the piston 15 to the right will reduce the obliquity of the cam plate 14 and thereby reduce the stroke of the pistons 13 until zero obliquity is obtained, whereupon continued movement in this direction will increase the stroke of the pistons 13 to provide increasing output in the reverse direction.

When it is required to move the piston 15 in the opposite direction, the control rod 17 is moved to the left as viewed in FIG. 1, until an internal groove 20 in the sleeve 45 is uncovered by the right-hand end of the valve 16. In this position, the groove 19 is out of register with the ports 18, thus preventing communication between the two sides of the piston 15. However, fluid can escape from the left-hand side of the piston via the groove 19, an axial bore 21, a passage 22 in the spool valve 16, a groove 20, a passage 23 and port 24 to the interior of the pump housing 10 which is maintained at a low pressure. As a result, the high pressure acting on the annular area of the piston 15 at its right-hand side will cause the piston to move to the left as viewed in the drawing, until communication between the groove 20 and the passage 23 is interrupted by the end of the spool valve 16. As in the opposite case, in order to maintain a continued movement of the piston 15 to the left, a continuous pull must be maintained upon the rod 17. The spool valve 16 is connected to the rod 17 by means of a collar 47 surrounding respectively the adjacent ends of the spool valve and rod and connected thereto respective by a pair of diametrical pins at right angles to one another to provide the equivalent of a limited universal connection. Moreover, the rod 17 extends through a plug 48 closing the end of the cylinder in the housing 10 containing the piston 15, and also extending into a body 49 secured to the housing 10 (FIG. 2).

Referring to FIG. 2, the rod 17 carried'at its outer end a pair of spaced abutment plates 25 between which is located a pin 26 extending laterally from a lever 27 pivoted at 28 upon a fixed bracket 29 on operable housing 10. The lever 27 forms part of a means permitting lost motion between the control rod 17 and the manually or otherwise operable means for controlling the rod 17. The other part of the means permitting lost motion comprises a bifurcated member 30 having arcuate recesses at the ends of its limbs which are held against complementary arcuate surfaces on the lever 27 by means of a coiled tension spring 31 interconnecting the two parts. The manually or otherwise opera le setting means is diagrammatically illustrated as being connected to the member 30 by a pivotal link 32, and it will be appreciated that if the rod 17 is moved axially when the rod 32 is fixed, the lever 27 can be moved angularly against the action of the spring 31 by permitting one of the arcuate surfaces of the lever 27 to move out of its recess on a limb of the'member 30 whilst depressing member 30 as a whole.

Also slidable in the housing is a stepped piston 33 which extends parallel to the rod 17. The step 33a of this piston is contained in a chamber 34 which is subjected to the output pressure of the pump. The pressure acting against the step 33a opposes the action of a pair of coiled compression springs 35,36 acting between the housing 10 and an abutment 37 on an extension of the piston 33.

Secured to a portion of the piston 33 outside the housing 10 is an arm 38 which is arranged to co-act with one of the abutment plates 25 in moving the rod 17 to cause a reduction in the pump stroke when the output pressure of the pump acting upon the step 33a exceeds a predetermined value and when the cam plate 14 of the pump is set at one inclination. The piston 33 also carries a pin 39 which is located in a slot at the lower end of a lever 40 fulcrummed at 41 on the bracket 29. The opposite end of the lever 40 is arranged to co-act with the other abutment plate 25 in moving the rod 17 in a direction to reduce the stroke of the pump when the pressure in the chamber exceeds the predetermined pressure, with the cam plate of the pump set to the opposite inclination.

Where the prime mover driving the pump drives a second or auxiliary pump and it is desired not to overload the prime mover, there may be provided a further piston 42 which is coaxially arranged with respect to the piston 33 and is contained in a chamber 43 which is subjected to the output pressure of the second or auxiliary pump. The piston 42 is arranged to bear against the piston 33 so that the piston 33 is moved by the combined output pressures of the two pumps. Thus, when the total load on the prime mover exceeds a predetermined value, the piston 33 will be moved in a direction to reduce the stroke of the main pump.

I claim:

1. A swash plate type pump comprising in combination a body, a rotor within the body having formed therein a plurality of equi-angularly spaced cylinders, a plurality of pistons occupying the cylinders respectively, an angularly adjustable cam plate with which the pistons co-act, a servo piston for moving the cam plate between opposite inclinations relative to the axis of rotation of the rotor, a pump stroke controlling member, valve means connected to said member for controlling the position of the servo piston, an abutment on said member, a pivoted lever operatively connected to said member, a part rockable relative to the lever against the action of resilient means, control means for setting said member, said control means being operatively connected to said part, a further piston subjected to the output pressure of the pump, an arm connected to the piston to co-act with the abutment in reducing the stroke of the pump against the action of said resilient means, when the pump output pressure pressure exceeds a predetermined pressure with the cam plate of the pump set at one inclination to the axis of rotation of the rotor, and a further lever connected to the piston so as to co-act with the abutment in reducing the stroke of the pump against the action of said resilient means, when the pump output pressure exceeds said predetermined pressure when the cam plate of the pump set at the opposite inclination to the axis of rotation of the rotor.

2. A swash plate type pump as claimed in claim 1 including a spring acting upon the further piston in opposition to the fluid pressure.

3. A swash plate type pump as claimed in claim 2 in which said part is bifurcated and has arcuate recesses at the ends of its limbs engaging upon complementary arcuate surfaces on the lever, said resilient means acting to hold the recesses against said arcuate surfaces. 4 

1. A swash plate type pump comprising in combination a body, a rotor within the body having formed therein a plurality of equiangularly spaced cylinders, a plurality of pistons occupying the cylinders respectively, an angularly adjustable cam plate with which the pistons co-act, a servo piston for moving the cam plate between opposite inclinations relative to the axis of rotation of the rotor, a pump stroke controlling member, valve means connected to said member for controlling the position of the servo piston, an abutment on said member, a pivoted lever operatively connected to said member, a part rockable relative to the lever against the action of resilient means, control means for setting said member, said control means being operatively connected to said part, a further piston subjected to the output pressure of the pump, an arm connected to the piston to co-act with the abutment in reducing the stroke of the pump against the action of said resilient means, when the pump output pressure pressure exceeds a predetermined pressure with the cam plate of the pump set at one inclination to the axis of rotation of the rotor, and a further lever connected to the piston so as to coact with the abutment in reducing the stroke of the pump against the action of said resilient means, when the pump output pressure exceeds said predetermined pressure when the cam plate of the pump set at the opposite inclination to the axis of rotation of the rotor.
 2. A swash plate type pump as claimed in claim 1 including a spring acting upon the further piston in opposition to the fluid pressure.
 3. A swash plate type pump as claimed in claim 2 in which said part is bifurcated and has arcuate recesses at the ends of its limbs engaging upon complementary arcuate surfaces on the lever, said resilient means acting to hold the recesses against said arcuate surfaces. 